The aromatic polyimide resin is a polymer mostly having an amorphous structure, and exhibits excellent heat resistance, chemical resistance, electrical properties, and dimensional stability due to its rigid chain structure. The polyimide resin is widely used as an electric/electronic material.
However, the polyimide resin has many limitations in use, because it is dark brown due to the formation of a CTC (charge transfer complex) of π electrons present in the imide chain.
In order to solve the limitations and obtain a colorless transparent polyimide resin, a method of restricting the movement of the π electrons by introducing a strong electron attracting group such as a trifluoromethyl (—CF3) group, a method of reducing the formation of the CTC by introducing a sulfone (—SO2—) group, an ether (—O—) group, or the like into the main chain to make a bent structure, or a method of inhibiting the formation of the resonance structure of the π electrons by introducing an aliphatic cyclic compound, has been proposed.
However, it is difficult for the polyimide resin according to the proposals to exhibit sufficient heat resistance due to the bending structure or the aliphatic cyclic compound, and a film prepared using the same still has limitations such as poor mechanical properties.